Source for C37A /C800 style mic capsules ?

[MatthewF]

Hi Bernd,

The mic circuit is the same topology as the original C37 i.e. a standard cathode follower. (For reference, the original circuit can be found here: http://www.rcrowley.com/sonyc37/images/diag.gif )

I changed some component values to compensate for my 150v B+ supply (I believe the original B+ may have been significantly higher) and to achieve ~60v capsule bias, which is what Dale recommended for his capsule.

To be specific, I used 68k and 3k3 resistors in the cathode and a 2.2µF output coupling cap. For the output transformer I used a sowter 3678 wired as 3:1 (5k:600R), and I omitted the resistor strapped across the primary. Also, I substituted a 5840 valve in place of the original 6AU6.

Best,

Matthew

 

[bernbrue]

Hi Matthew,
I´m modding a cheap chinese mic according to your description above right now. I know, it´s always difficult to describe sound, but do mics with a cathode follower sound specific in comparision to lets say C12 modded Apex 460? My microphone is quite small and I have to úse one of these tiny beyer transformers which has a 1:5 ratio. Would it be ok to use a transformer which such a high ratio in a cathode follower circuit? Transformers with lower ratio would probably be better in such a circuit, but I haven´t got one that fits in size. I found a nice way to mount the EF732 (5840) tube and really eager to try it out. Any comments are appreciated!
regards
Bernd